Recent talks given

Why holes are not like electrons, and what that may have to do
with superconductivity

USC condensed matter seminar, March 23, 2001
Abstract:
Most Hamiltonians that are used to describe many-body physics in solids
are electron-hole symmetric. Yet I argue that nature makes an
enormous difference between electrons and holes. In particular,
elements with one electron outside a closed shell make good metals,
those with one hole in a filled shell are insulators. Why are the
holes in Cl less mobile than the electrons in Na? What breaks the
symmetry between electrons and holes in nature? I propose that the
answer is that hole carriers in solids are heavily dressed, while electron
carriers are undressed. Inclusion of this physics leads to a new class
of Hamiltonians, and to a theory of
'hole superconductivity' whereby heavily
dressed hole carriers pair in order to undress and become more like
electrons, hence more mobile.
The theory describes a phenomenology of superconductivity that has
an eerie resemblance to many aspects of the phenomenology seen in high Tc
cuprates. Based on these results I propose that electron-hole asymmetry is the
key to superconductivity.

Why can only hole conductors be high temperature superconductors ?

University of Wisconsin Herb Materials Physics Seminar , March 29, 2001
Abstract:
There is strong empirical evidence that superconductivity is favored when the charge carriers in the normal state of a metal are holes rather than electrons. Examples are high T_c cuprates, C_60 (see Batlogg et al, Nature 408, 549 (2000)), and the elements: out of 40 nonmagnetic metallic elements, 16 out of 17 non-superconductors have negative Hall coefficient (indicating dominance of electron carriers), and 18 out of 23 superconductors have positive Hall coefficient (indicating dominance of hole carriers). Why is this so? The conventional theories of superconductivity do not differentiate between electron and hole carriers. We will show that there is a simple and intuitive explanation for it. This explanation leads to a theory of superconductivity(1) that exhibits many aspects of the phenomenology seen in high T_c cuprates. The theory makes predictions for various experimentally observable quantities that will be compared with experimental results where available.
(1) References in: http://physics.ucsd.edu/~jorge/hole.html

Why holes are not like electrons, and what that may have to do
with superconductivity

UCLA condensed matter seminar, December 5, 2001
Abstract:
Ever since Heisenberg first proposed the 'hole' concept in 1931 based
on Pauli's exclusion principe, electrons and holes have been
regarded as equivalent quasiparticles in condensed matter.
Here we argue instead that electrons and holes are fundamentally
different objects. The difference, which arises due to
electron-electron interactions and can be understood at the level
of a single hydrogen atom, is that holes are heavily
dressed while electrons are undressed. In electronic
energy bands in solids, as the density of electrons increases the
Fermi level rises from the bottom of the band, quasiparticles
turn from electrons to holes and become increasingly dressed.
Conversely, as the density of holes increases
quasiparticles turn from holes to electrons and gradually undress.
Pairing of holes increases the local hole density and leads
to hole undressing, and to superconductivity. Whether this
mechanism of superconductivity may apply to any or all
materials will be discussed.

Dynamic Hubbard models: a new class of model Hamiltonians for
interacting electrons

Departamento de Teoria de la Materia Condensada,
Instituto de Ciencia de Materiales de Madrid, CSIC.
September 19, 2002.
Abstract:
The Hubbard model is generally believed to be the simplest model
to describe strongly correlated electrons in solids. We argue that
it is fundamentally flawed, and in particular cannot be used to
describe electrons in energy bands that are more than half-filled.
We introduce a new class of model Hamiltonians, 'dynamic Hubbard
models', to describe interacting electrons in bands with arbitrary
filling. New physics emerging from these models is discussed, and
numerical results for small clusters are presented. The results
have important implications for the understanding of superconductivity.

Quasiparticle undressing: a new route to collective effects in solids

Concepts in Electron Correlation,
September 29th - October 3rd 2002,
Hvar, Croatia
Abstract
The carriers of electric current in a metal are quasiparticles dressed by electron-electron interactions, which
have a larger effective mass $m^*$ and
a smaller quasiparticle weight $z$ than non-interacting carriers. If the momentum dependence of the self-energy can be neglected, the effective mass enhancement and quasiparticle weight of quasiparticles at the Fermi energy are
simply related by $z=m/m^*$ ($m$=bare mass). We propose that both superconductivity and ferromagnetism in metals are driven by
quasiparticle 'undressing', i.e., that the correlations between quasiparticles that give rise to the collective state
are associated with an increase in $z$ and a corresponding decrease in $m^*$ of the carriers. Undressing gives rise to
lowering of kinetic energy, which provides the condensation energy for the collective state.
In contrast, in conventional descriptions of superconductivity and ferromagnetism the transitions to these collective states result in $increase$ in kinetic energy of the carriers and are driven by lowering of potential energy and exchange energy respectively.
Experimentally this undressing physics should manifest itself in transfer of spectral weight from high to low frequencies
in one- and two-particle spectral functions as the collective state develops, measured by photoemission and optical absorption, and in violation of low frequency sum rules. The high frequency scale where the spectral weight is transferred from is much higher than and unrelated to the energy scale of the condensation energies and of $T_c$. Experimental evidence for this physics has been seen in high $T_c$ cuprate
superconductors[1,2,3,4,5] and in certain ferromagnets[6,7,8]. It is proposed that the dominant quasiparticle dressing originates in Coulomb interaction between the carrier and the neighboring electronic site and bond charge, and that undressing in superconductors and ferromagnets results from the decrease in site and bond charge around the carrier associated with hole pairing and with spin polarization respectively. Model Hamiltonians generically called 'dynamic Hubbard models' will be discussed to describe this physics, and numerical results will be presented. The relation of parameters in the Hamiltonians to the physics of real atoms will be discussed.
[1] H. J. A. Molegraaf et al, Science {\bf 295}, 2239 (2002).
[2] A.F. Santander-Syro et al, cond-mat/0111539 (2001), Europhys.Lett.62, 568 (2003)
[3] D.N. Basov et al, Science {\bf 283}, 49 (1999).
[4] H. Ding et al, Phys. Rev. Lett. {\bf 87}, 227001 (2001).
[5] P. D. Johnson et al, Phys. Rev. Lett. {\bf 87}, 177007 (2001).
[6] L. Degiorgi et al, Phys. Rev. Lett. {\bf 79}, 5134 (1997); Phys.Rev. B{\bf 65}, 121102 (2002).
[7] Y. Okimoto et al, Phys.Rev. B{\bf 57}, 9377 (1998).
[8] E.J. Singley et al, Phys.Rev.Lett. {\bf 89}, 097203 (2002) .

Electron-hole asymmetry in solids and its implications for superconductivity

University of Bristol, November 13, 2002
Abstract:
Ever since Heisenberg first introduced the 'hole' concept in 1931 based on Pauli's exclusion principe, electrons and holes have been regarded as equivalent quasiparticles in condensed matter. Instead I argue that electrons and holes are fundamentally different objects. The difference between them arises because of electron-electron interactions and can be understood at the level of a single hydrogen atom. Models generally used to describe electronic correlations in solids, such as the Hubbard model, do not describe this fundamental asymmetry. I propose a new class of model Hamiltonians, bdynamic ubbard modelsb, as the simplest class of models that describe this fundamental aspect of electronic correlation effects. These models predict that only hole carriers can give rise to superconductivity in solids. I review empirical and experimental evidence on superconductors that supports this and other predictions of the models.

What is wrong with the Hubbard model, and how to fix it

Max Planck Institute for the Physics of Complex Systems, Dresden,
November 21, 2002.
Abstract:
The Hubbard model is widely accepted as the simplest model describing the essential physics of electronic correlations in solids. However, it has a fundamental flaw: while it accounts for the fact that 2 electrons in the same atomic orbital pay an energy cost of U due to their mutual Coulomb repulsion, it fails to describe the fact that those 2 electrons are described by a correlated wave function rather than a single Slater determinant, precisely because of their Coulomb interaction. This is an elementary fact, well known and studied for the case of atoms and molecules; however, its importance for the physics of the solid state has not been recognized. In particular it implies that there exists a fundamental asymmetry between electrons and holes in electronic energy bands. This leads to the prediction that only hole carriers can give rise to superconductivity in solids. In fact, the empirical observation that hole carriers in solids favor superconductivity was made long ago(1) but never explained. I propose a new class of model Hamiltonians, dynamic Hubbard models, that capture this essential physics that is missing in the conventional Hubbard model. I discuss results and predictions for these models and their relationship with experimental observations on superconducting materials.
(1) Kikoin and Lazarev, ~1940; R. Feynman, Rev.Mod.Phys.29, 205 (1957) ; I.M. Chapnik, Sov.Phys.Dokl. 6, 988 (1962).

Dynamic Hubbard Models: An Ideal Playground for DMFT

Theory of hole superconductivity

New Theories, Discoveries, and Applications of Superconductors and Related Materials
(New3SC-4), San Diego, January 26-21, 2003
Abstract:
There exists a fundamental asymmetry between electrons and holes in condensed matter. This can be simply understood at the level of a single He atom , as arising from the difference in the nature of the electronic states of neutral and doubly ionized He. It leads to the conclusion that in electronic energy bands holes are always more bdressedb than electrons. This physics is not described by conventional Hubbard models but by a new class of models recently proposed, bdynamic Hubbard modelsb. These models predict that only hole carriers can give rise to superconductivity, through the process of bhole undressingb. When both electron and hole carriers coexist at the Fermi energy, holes will pair and drive also the electrons superconducting, resulting in pairs with different binding energies, hence multiple gaps. Upon application of a magnetic field electron pairs will break up before hole pairs, resulting in sign reversal of the Hall coefficient. Clear experimental evidence that hole pairing drives superconductivity is seen in cuprates, MgB2, and many other, including elemental, superconductors. Clear experimental evidence that hole pairing leads to undressing of carriers is seen in the cuprates. Clear experimental evidence that dressed holes turn into undressed electrons upon pairing is seen in both conventional and high Tc superconductors. This universal theory of superconductivity provides well-defined guidelines for the search for new high T_c superconducting compounds and will be reviewed in this talk.

Superconductors as giant atoms

Presented at the meeting 'Highlights in Condensed Matter Physics' in honor of the 60th birthday of Prof. Ferdinando Mancini , May 9-11, 2003, Salerno, Italy
Abstract:
In atoms, electrons respond to an applied magnetic field by acquiring a velocity
-eA/m_ec, with A the magnetic vector potential, e the electron charge and m_e the free electron mass. The same is true in superconductors according to London's theory and to experiment. Hence we argue that a metal in the superconducting state should be regarded as a 'giant atom' (1), and that superfluid electrons behave as negative bare electrons in atoms, rather than as dressed Bloch-Landau quasiparticles whose charge sign (i.e. electron- or hole-like) depends on the band structure. The correct theory of superconductivity has to describe the 'undressing' of the normal state quasiparticles becoming free-electron-like in the superfluid state. This physics is not part of the standard BCS-Eliashberg theory of superconductivity, but it is described in the theory of hole superconductivity (2). The theory predicts that only hole carriers in the normal state can give rise to superconductivity, and that superconductivity is driven by undressing and kinetic energy lowering, in agreement with old ideas of Schafroth (1954) and Bardeen (1950) and recent experiments. Because superconducting bodies, unlike atoms, can be multiply connected one can observe in superconductors properties that do not exist in atoms such as persistent charge currents. As in atoms, we predict that the electric charge distribution in superconductors is not homogeneous. We also predict that macroscopic spin currents should exist in superconductors arising from macroscopic spin-orbit coupling, and discuss experimental ways to detect them.
(1) J.E. Hirsch, Phys.Lett. A 309, 457 (2003).
(2) http://physics.ucsd.edu/~jorge/hole.html

Electron-hole asymmetry and superconductivity

The fundamental role of charge asymmetry in superconductivity

Temple University, February 7, 2005
Abstract:
Superconductivity occurs predominantly in materials where the charge carriers in the normal state are holes rather than electrons. Examples are high Tc cuprates, magnesium diboride, and the elemental superconductors. Other clear manifestations of charge asymmetry in superconductivity are asymmetric tunneling characteristic in cuprates and properties of rotating superconductors. However the importance of charge asymmetry for superconductivity has not been widely recognized: BCS theory of conventional superconductivity as well as new theories proposed to describe high Tc cuprates do not differentiate between electron and hole carriers. I will discuss an alternative theory of superconductivity that has charge asymmetry as its fundamental ingredient. The theory explains many experimental observations, including the remarkable Tao effect, makes testable predictions, and provides new guidelines for the search for new high Tc superconducting compounds.

Explanation of the Tao effect

2005 APS March Meeting,
Thursday, March 24, 2005
LACC - 507, 11:15 AM-11:27 AM
Abstract:
Tao and coworkers discovered that in an applied electric field superconducting microparticles aggregate to form balls of macroscopic dimensions$^{(1)}$. The phenomenon appears to be as general as the Meissner effect. Within the conventional theory of superconductivity electrostatic fields do not penetrate into superconductors and the observed effect would not be expected. We propose an explanation of the effect based on an alternative description of the electrodynamics of superconductors recently proposed$^{(2)}$, that results from the unconventional theory of `hole superconductivity'. In our theory a spontaneous electrostatic field exists inside superconductors and if the sample is not spherical also outside. Experiments to test the theory will be discussed. (1) R. Tao, X. Xu and E. Amr, Physica C 398, 78 (2003) and references therein. (2) J.E. Hirsch, Phys.Rev. B 69, 214515 (2004) and references therein.

Superconductors, Tao balls, and macroscopic atoms

San Diego State University, September 16, 2005
Abstract:
When Rongjia Tao recently applied an electric field to millions of superconducting microparticles in suspension he discovered a surprising new effect(1): they fly towards each other, clumping up into a tightly bound round ball of mm-size radius. Neither London nor BCS, the founders of the currently established understanding of superconductivity, expected this, nor do they have any clue as to why this occurs. To me, Tao balls look like giant atoms, and the phenomenon is a manifestation of the fundamental charge asymmetry of matter that is at the root of the phenomenon of superconductivity according to the unconventional theory of "hole superconductivity"(2). I will present the essential elements of this theory, developed over the past 15 years, describe how it explains the "Tao effect", and discuss other experiments that could be done to decide on its ultimate validity or invalidity.
(1) R. Tao, X. Xu and E. Amr, Physica C 398, 78 (2003) and references therein.
(2) J.E. Hirsch, Phys.Rev. Lett. 94, 187001 (2005) and references therein.

Concepts in Electron Correlation,
September 30th - October 5th 2005,
Hvar, Croatia
Abstract:
The theory of hole superconductivity(1) has been proposed as an alternative to the
conventional theory of superconductivity to describe both high Tc and conventional
superconductors. It has many elements in common with the conventional London-
BCS theory as well as profound differences. In particular,
the macroscopic electrodynamic equations governing superconductors are predicted to be different in the new
theory, which leads to prediction of unexpected effects: penetration of electric fields
into superconductors, spontaneous electric fields around superconductors, spherical
aggregation of superconducting microparticles in an electric field (Tao effect), spin
currents in the ground state of superconductors, changes in the plasmon dispersion
relation. These predictions are experimentally testable. Other new and unexpected
effects will be discussed.
(1) References in http://physics.ucsd.edu/ jorge/hole.html

Why are Physicists Silent? The Dangers of New US Nuclear Weapons Policies

Electric Fields in Superconductors: an Explanation of the Tao Effect

94th STATISTICAL MECHANICS CONFERENCE, Rutgers University, December 19, 2005
Abstract:
When Rongjia Tao recently applied an electric field to millions
of superconducting microparticles in suspension he discovered a
surprising new effect(1): they fly towards each other, clumping up
into a tightly bound round ball of mm-size radius. Within the
conventional theory of superconductivity electrostatic fields do
not penetrate into superconductors and the observed effect would not
be expected. I propose an explanation of the effect based on an
alternative description of the electrodynamics of superconductors
that results from the unconventional theory of `hole superconductivity'
(2).
(1) R. Tao et al, Phys. Rev. Lett. 83, 5575-5578 (1999)
(2) References in J.E. Hirsch, http://physics.ucsd.edu/~jorge/hole.html

What the h-index is and why it matters

Do superconductors violate basic laws of physics?

San Diego State University, September 15, 2006
Abstract:
I will show that superconductors violate at least one basic law of
physics: either Lenz's law, or angular momentum conservation, or Newton's
second law. For those that have faith in theory I will explain how this
conundrum can be resolved with least collateral damage. For those
that don't I will discuss a simple experiment that can decide between the
different possibilities, that could have been done many years ago but hasn't.

Nucleoholic and dangerous: the US and its nuclear weapons

Osher Lifelong Learning Institute, UCSD, October 5, 2006
Abstract:
Like a recovering alcoholic, the US has been nuclear-sober for 60 years.
However, changes in the US nuclear weapons policies under the Bush
administration, characterized as "a radical departure from the past" by Linton
Brooks, the chief US administrator of the nuclear weapons arsenal, are bringing
us dangerously close to relapse. I will discuss the rationale as well as the
irrationality and enormous danger entailed in the new US nuclear policies and
plans, and why they may be put into practice in a confrontation with
Iran. I will also discuss why non-proliferation initiatives and efforts for
reduction and ultimate elimination of nuclear weapons arsenals increase
rather than reduce the danger, and what should be done instead.

On a new effect observed in the transition to the supraconductive state

Fritz Haber Institute, Berlin, March 23, 1937 2007
Abstract:
Professor Walther Meissner and Herr Dr. Robert Ochsenfeld in Berlin
recently discovered a new effect in supraconductors: the magnetic
field intensity in the neighborhood of a supraconducting body changes
when the body is cooled in an external magnetic field. This surprising
effect appears to violate the Maxwellian theory of electromagnetism as
well as the conservation of angular momentum required by Newtonian
theory. However I will propose an explanation of Meissner's observation
that is consistent with Maxwellian and Newtonian theory. This
explanation requires that spontaneous electric fields exist inside
supraconductors in the absence of externally applied fields. Theoretical
and experimental evidence in favor of this strange hypothesis will
be presented, and new experiments will be proposed to test its validity.

The h-index: how useful is it as a measure of scientific achievement?

DPG Meeting, Regensburg, Germany, March 26-30, 2007
Abstract:
The h-index was proposed in 2005 as a succinct way to quantify
an individual's scientific research output. It has generated
considerable interest not only in physics but also in other scientific
disciplines, and has recently been implemented in the ISI Web of Science.
Several extensions of the original concept have also been proposed. I will
discuss various properties of the h-index, what I view as its advantages
over other indicators and potential disadvantages, and whether it is a
good predictor of future achievement.

Will the U.S. Use Nuclear Weapons in a Military
Confrontation with Iran? Why Congress Needs to
Confront This Possibility

GROSSMONT COLLEGE POLITICAL ECONOMY WEEK, APRIL 30-MAY 4, 2007,
San Diego, California

How hole conductors become electron superconductors

High-Temperature Superconductivity in Cuprates,
Original Concept and New Developments, October 7 - 12, 2007
Tbilisi, Georgia
Abstract:
Holes dominate the normal state transport in high Tc hole-doped cuprates,
in electron-doped cuprates in the regime where they become
superconducting(1), in the relatively high Tc MgB2, and in the vast
majority of "conventional" superconductors. Electrons carry the
electric current in the superconducting state of those
materials (as revealed by London moment measurement and other experiments)
and in the normal state of materials that never become superconducting
such as alkali and noble metals. The discovery of high Tc superconductivity
in cuprates by Bednorz and Muller and subsequent developments shone a
bright light into the key role of charge asymmetry in superconductivity
generally, which had escaped attention before. The theory of hole
superconductivity(2) is proposed to apply to all superconducting materials
and explains those as well as many other observations such as asymmetric
tunneling spectra(3) and optical spectral weight transfer. It proposes
that superconductivity originates in pairing and condensation of
electron-hole-asymmetric electronic polarons, driven by kinetic energy
lowering. A new class of model Hamiltonians grounded in basic ubiquitous
atomic physics, "dynamic Hubbard models", describes the microscopic physics.
The theory predicts a novel inhomogeneous charge distribution in superconductors, with excess negative charge near the surface.
With respect to "At the extreme forefront of research in superconductivity
is the empirical search for new materials" the theory dictates that the
search for high Tc superconductivity should be restricted to materials
where normal state transport occurs in negatively charged
substructures (eg planes) with closely spaced anions and almost filled
energy bands.
(1)Y. Dagan and R.L. Greene, " Hole superconductivity in the electron-doped superconductor Pr2-xCexCuO4", Phys.Rev. B76, 024506 (2007).
(2)References in: http://physics.ucsd.edu/~jorge/hole.html
(3) F. Marsiglio and J.E. Hirsch, "Tunneling asymmetry: A test of superconductivity mechanisms", Physica C 159, 157 (1989); P.W. Anderson and N.P. Ong, "Theory of asymmetric tunneling in the cuprate superconductors", J. Phys. Chem. Solids 67, 1 (2006).

The Meissner Effect, the Tao Effect, and Other Unexplained Riddles of Superconductors

UCSD Physics Colloquium, January 24th, 2008
Abstract:
The Meissner effect, discovered in 1933, is the process by which a superconductor expels a magnetic field from its interior as it makes the transition from the normal to the superconducting state. It is a hallmark of superconductivity. It is generally believed that the Meissner effect is throughly explained by theory: phenomenologically by London's 1935 theory and microscopically by BCS (1957) theory. Instead, I will try to convince you that the Meissner effect is a fundamental unexplained riddle within conventional London-BCS theory. Another unexplained effect that occurs when strong electric fields are applied to superconductors was discovered by Rongjia Tao in 1999. Finally, many more unsolved riddles resulted from the 1986 discovery of high temperature superconductivity in cuprate oxides. I will discuss the basic principles of the unconventional theory of hole superconductivity, proposed to describe both high temperature superconductivity in cuprates as well as superconductivity of conventional materials. The theory offers an explanation for the Meissner effect and the Tao effect, and predicts a new as yet unseen physical phenomenon in all superconductors, the "Spin Meissner effect".

Spin Meissner Effect in Superconductors and the Origin of the Meissner Effect

Link to talk here
Conference on Concepts in Electron Correlation
September 24 - 30, 2008 Hvar, Croatia
Abstract:
The expulsion of magnetic flux from the interior of a metal that becomes superconducting
(Meissner effect) was discovered experimentally in 1933. Contrary to conventional
wisdom, I argue that it is impossible to explain this effect within the accepted framework of
London-BCS theory: one would have to assume either violation of Lenz's law, or violation
of angular momentum conservation, or both. Instead, I propose that the outward motion of
magnetic field lines as a metal goes superconducting reflects and is a consequence of outward
motion of electric charge, just like would happen in a classical plasma (Alfven's theorem).
According to the theory of hole superconductivity[1], metals become superconducting because
they are driven to expel excess negative charge from their interior. This is why high
Tc occurs in the highly negatively charged (CuO2)=, B- and (FeAs)- planes of cuprates,
MgB2 and iron arsenides respectively, and why NIS tunneling spectra are asymmetric, with
larger current for a negatively biased sample. How to reconcile the resulting macroscopic
charge inhomogeneity with the supposed non-existence of macroscopic electric fields in the
interior of superconductors will be discussed in the talk. Charge expulsion is also associated
with an expansion of the electronic wavefunction and a decrease in the kinetic energy associated
with quantum confinement, consistent with observations[2]. In addition to explaining
the Meissner effect, this physics gives rise to a Spin-Meissner effect[3]: a macroscopic spin
current is predicted to flow near the surface of superconductors in the absence of applied
external fields, of magnitude equal (in the appropriate units) to the critical charge current
of the superconductor. The orbital angular momentum of each electron in the spin
current equals its spin angular momentum. This physics also provides a geometric interpretation
of the difference between type I and type II superconductors, and predicts that
the macroscopic electric field in the interior of superconductors equals the thermodynamic
critical magnetic field Hc or Hc1 for type I and type II superconductors respectively. These
predictions are theoretically and experimentally testable.
[1] References in http://physics.ucsd.edu/ jorge/hole.html
[2] H. J. A. Molegraaf et al, Science 295, 2239 (2002).
[3] J.E. Hirsch, Europhys. Lett. 81, 67003 (2008); Ann. Phys. (Berlin) 17, 380 (2008).

Second CoMePhS Workshop in
Controlling Phase Separation in Electronic Systems,
Nafplion, Greece - September 30th - October 4th 2008
Abstract:
Superconductivity occurs in systems that have a lot of negative charge: the
highly negatively charged (CuO2)= planes in the cuprates, negatively charged (FeAs)-
planes in the iron arsenides, and negatively charged B- planes in magnesium
diboride. And, in the nearly filled (with negative electrons) bands of almost
all superconductors, as evidenced by their positive Hall coefficient in the
normal state. Why? No explanation for this charge asymmetry is provided by
the conventional theory of superconductivity, within which the sign of electric
charge plays no role. Instead, the sign of the charge carriers plays a key
role in the theory of hole superconductivity[1], according to which metals
become superconducting because they are driven to expel negative charge (electrons)
from their interior. This is why NIS tunneling spectra are asymmetric, with larger
current for negatively biased samples, as was predicted by this theory[2] long
before it was experimentally verified[3]. The theory also explains the (otherwise
unexplained[4]) Meissner effect: as electrons are expelled towards the surface in
the presence of a magnetic field, the Lorentz force imparts them with azimuthal
velocity, thus generating the surface Meissner current that screens the interior
magnetic field. In type II superconductors, the Lorentz force acting on
expelled electrons that don't reach the surface gives rise to the azimuthal
velocity of the vortex currents. In the absence of applied magnetic field,
expelled electrons still acquire azimuthal velocity, due to the spin-orbit
interaction, in opposite direction for spin-up and spin-down electrons: the "Spin
Meissner effect"[5]. This results in a macroscopic spin current flowing near the
surface of superconductors in the absence of applied fields, of magnitude equal to
the critical charge current. Charge expulsion also gives rise to an interior
electric field and to excess negative charge near the surface. In strongly type II
superconductors this physics should give rise to charge inhomogeneity and spin
currents throughout the interior of the superconductor, to large sensitivity
to (non-magnetic) disorder and to a strong tendency to phase separation.
References
[1] References in http://physics.ucsd.edu/~jorge/hole.html.
[2] F. Marsiglio and J.E. Hirsch, "Tunneling Asymmetry: a Test of Superconductivity Mechanisms", Physica C 159, 157 (1989).
[3] Y. Kohsaka et al, Science 315, 1380 (2007).
[4] J.E. Hirsch, J. Phys. Cond. Matt. 20, 235233 (2008).
[5] J.E. Hirsch, Europhys. Lett. 81, 67003 (2008); Ann. Phys. (Berlin) 17, 380 (2008).

Meissner effect and Spin Meissner effect in superconductors

XIV Simposio en Ciencia de Materiales
Centro de Nanociencias y Nanotecnologia
Universidad Nacional Autonoma de Mexico
Ensenada, Baja California,
Mexico, Febrero 10-13, 2009
Abstract:
The Meissner effect is the spontaneous generation of a surface charge current in a metal that makes a transition from the normal to the superconducting state in the presence of an external magnetic field. It was discovered experimentally in 1933 and supposedly explained by BCS-London theory by 1957. I will argue that the Meissner effect is not explained by conventional BCS-London theory, hence it remains an outstanding puzzle calling for an explanation. Another outstanding puzzle is the origin of high temperature superconductivity in cuprate oxides discovered in 1986 by Bednorz and Muller. I will discuss the basic principles of the unconventional ``theory of hole superconductivity'' that is proposed to apply to all superconductors and (i) explains the puzzle of high Tc superconductors, (ii) explains the origin of the Meissner effect, and (iii) predicts a new as yet undetected effect in superconductors, the ``Spin Meissner effect'': the spontaneous generation of a surface spin current in a metal that makes a transition from the normal to the superconducting state in the absence
of external fields, resulting in the existence of a surface spin current in the ground state of superconductors.

h index and hbar index

NSF workshop on "Scholarly Evaluation Metrics: Opportunities and
Challenges", Washington DC, December 16th, 2009
Abstract: The h index and the hbar index were discussed.
h is the number of papers of an individual that have citation count
larger than or equal to the h of that individual
hbar is the number of papers of an individual that have citation count
larger than or equal to the hbar of each of the coauthors of each paper

Explanation of the Meissner Effect and Prediction of a Spin Meissner Effect in Superconductors

UCLA condensed matter seminar, January 20th, 2010
Abstract:
When a metal is cooled into the superconducting state in the presence of a static external magnetic field, a surface current starts flowing spontaneously that creates a magnetic field equal and opposite to the applied magnetic field in the interior of the body (Meissner effect). What is the force that generates this surface current, and how can it overcome Faraday's electric force that opposes it? How is angular momentum conserved? I argue that the conventional BCS-London theory of superconductivity cannot answer these questions.

I propose an explanation of the Meissner effect that requires new electrodynamic equations for superconductors, that are symmetric in electric and magnetic fields. These equations predict the existence of a spontaneous electric field in the interior of superconductors and the generation of a surface spin current when a metal is cooled into the superconducting state in the presence or absence of an external magnetic field. I call this the "Spin Meissner Effect" and predict that it is a universal property of all superconductors. The speed of the carriers of the spin current is hbar/(4 x electron mass x London penetration depth).

I discuss the relation of this physics to the theory of `hole superconductivity', to what extent it is supported or contradicted by existing experiments, and how it furnishes criteria that can help find new higher temperature superconductors.

Charge expulsion and Spin Meissner Effect in Superconductors

APS March meeting, Portland, Oregon, March 2010
(Link to abstract here)
Abstract:
I argue that the Meissner effect (expulsion of magnetic field from the interior of a metal going into the superconducting state) cannot be explained by the conventional BCS-London theory, hence that BCS-London theory is incorrect[1]. The theory of hole superconductivity explains the Meissner effect as arising from the expulsion of negative charge from the interior of the superconductor towards the surface, resulting in a non-homogeneous charge distribution, a macroscopic electric field in the interior, and a spin current near the surface (Spin Meissner effect). Electrodynamic equations describing this scenario will be discussed[2]. In the charge sector, these equations are related to electrodynamic equations originally proposed by the London brothers[3] but shortly thereafter discarded by them[4]. [1] J.E. Hirsch, Physica Scripta 80, 035702 (2009). [2] J.E. Hirsch, Ann. Phys. (Berlin) 17, 380 (2008). [3] F. London and H. London, Proc. R. Soc. London A149, 71 (1935). [4] H. London, Proc. R. Soc. London A155, 102 (1936).

Superconductors as big atoms, and
atoms as small superconductors

UCSD Condensed Matter seminar, October 13th, 2010
Abstract:
According to Bohr's correspondence principle, microscopic quantum
behavior should smoothly morph into macroscopic classical behavior.
Superconductivity is a unique state of matter where quantum mechanics
manifests itself at a macroscopic scale. As such, it presents us with the
unique challenge to understand the same phenomenon from both a
quantum and a classical point of view. Together with this challenge
comes a unique opportunity: superconductors give us a `window' through
which we can peer into the microscopic world and understand it in a new
way. In this connection, I will discuss what the theory of hole
superconductivity can teach us about angular momentum, quantum phase,
quantum zero-point motion and double-valuedness of wavefunctions.
Instead, the conventional BCS-London theory of superconductivity ignores
this challenge and as a consequence cannot teach us about either realm.

APS March meeting, Dallas, Texas, March 2011
(Link to abstract here)
(Link to talk here (pdf, 8.6MB))
Abstract:
The vast majority of superconducting materials have positive Hall coefficient in the normal state, indicating that hole carriers dominate the normal state transport. This was noticed even before BCS theory, and has been amply confirmed by materials found since then: the sign of the Hall coefficient is the strongest normal state predictor of superconductivity. In the superconducting state instead, superfluid carriers are always electron-like, i.e. negative, as indicated by the fact that the magnetic field generated by rotating superconductors is always parallel, never antiparallel, to the body's angular momentum (``London moment''). BCS theory ignores these facts. In contrast, the theory of hole superconductivity, developed over the past 20 years (papers listed in http://physics.ucsd.edu/$\sim $jorge/hole.html) makes charge asymmetry the centerpiece of the action. The Coulomb repulsion between holes is shown to be smaller than that between electrons, thus favoring pairing of holes, and this fundamental electron-hole asymmetry is largest in materials where the conducting structures have \textit{excess negative charge}, as is the case in the cuprates, arsenides and MgB2. Charge asymmetry implies that superconductivity is driven by lowering of kinetic energy, associated with expansion of the carrier wavefunction and with \textit{expulsion of negative charge} from the interior to the surface of the material, where it carries the Meissner current. This results in a macroscopic electric field (pointing outward) in the interior of superconductors, and a macroscopic spin current flowing near the surface in the absence of external fields, a kind of macroscopic zero point motion of the superfluid (spin Meissner effect). London's electrodynamic equations are modified in a natural way to describe this physics. It is pointed out that a dynamical explanation of the Meissner effect \textit{requires} radial outflow of charge in the transition to superconductivity, as predicted by this theory and not predicted by BCS. The theory provides clear guidelines regarding where new higher T$_{c}$ superconductors will and will not be found.

Meissner effect and Spin Meissner effect in superconductors

SLAFES XX, Maragogi, AL, March 27-23, 2011
(conference website)
Abstract:
The Meissner effect[1] and the Spin Meissner effect[2] are the spontaneous
generation of charge and spin current respectively near the surface of a metal
making a transition to the superconducting state. The Meissner effect is well
known but, I argue, not explained by the conventional theory, the Spin Meissner
effect has yet to be detected. I propose that both effects take place in all
superconductors. The speed of the carriers of the predicted spin current is
the speed associated with the critical charge current, since superconductivity
is destroyed when the magnetic field is large enough to bring one component
of the spin current to a halt. I show that both effects can be understood
under the assumption that a metal expels negative charge from the interior
to the surface in the transition to superconductivity[3], a phenomenon which
is predicted by the theory of hole superconductivity, proposed to describe
all superconductors[4, 5] and is not predicted by conventional BCS theory.
The cost in electrostatic energy due to charge separation is compensated by
the lowering of quantum kinetic energy of the system, and the spin current
results from Rashba-like coupling to the resulting internal electric fi eld. The
associated electrodynamics[6] is qualitatively different from London electrodynamics,
yet can be described by a small modification of the conventional
London equations. The stability of the superconducting state and its macroscopic
phase coherence hinge on the fact that the orbital angular momentum
of the carriers of the spin current is found to be exactly hbar/2, indicating a
topological origin. The electric field resulting from the expulsion of negative
charge is found to have magnitude equal to Hc1 (in cgs units) near the surface.
The ground state of superconductors is thus proposed to possess rotational
zero-point motion, suggesting that the same is true in other systems. The
simplicity and universality of our theory argue for its validity. I will discuss
how the existence of superconductivity in various classes of materials can
be understood within our theory, existing experimental evidence for it, and
experiments that should be done to prove it or disprove it.
[1] W. Meissner and R. Ochsenfeld, Naturwissenschaften 21, 787 (1933).
[2] J. E. Hirsch, Europhys. Lett. 81, 67003 (2008).
[3] J. E. Hirsch, Phys.Rev. B 68, 184502 (2003).
[4] J. E. Hirsch and F. Marsiglio, Physica C 162-164, 591 (1989).
[5] J. E. Hirsch, J. Phys. Chem. Solids 67, 21 (2006).
[6] J. E. Hirsch, Phys.Rev. B 69, 214515 (2004); Ann. Phys. (Berlin) 17, 380
(2008).

Correcting 100 years of misunderstanding: electric fields in superconductors, hole superconductivity, and the Meissner effect

8th International Conference on Stripes and High Tc Superconductivity STRIPES 11, Rome, July 10th-16th, 2011
Abstract:
From the outset of superconductivity research it was assumed that no electrostatic fields could exist inside superconductors, and this assumption was incorporated into conventional London electrodynamics. Yet the London brothers themselves initially (in 1935) had proposed an electrodynamic theory of superconductors that allowed for static electric fields in their interior, which they unfortunately discarded a year later. I argue that the Meissner effect in superconductors necessitates the existence of an electrostatic field in their interior, originating in the expulsion of negative charge from the interior to the surface when a metal becomes superconducting. The theory of hole superconductivity predicts this physics, and associated with it a macroscopic spin current in the ground state of superconductors ("Spin Meissner effect"), qualitatively different from what is predicted by conventional BCS-London theory. A new London-like electrodynamic description of superconductors is proposed to describe this physics. Within this theory superconductivity is driven by lowering of quantum kinetic energy, the fact that the Coulomb repulsion strongly depends on the character of the charge carriers, namely whether electron- or hole-like, and the spin-orbit interaction. The electron-phonon interaction does not play a significant role, yet the existence of an isotope effect in many superconductors is easily understood. In the strong coupling regime the theory appears to favor local charge inhomogeneity. The theory is proposed to apply to all superconducting materials, from the elements to the high Tc cuprates and pnictides, is highly falsifiable, and explains a wide variety of experimental observations.

Kinetic energy driven superconductivity and the origin of the Meissner effect in new and old superconductors

E-MRS 2011 Fall Meeting, Warsaw, Poland, September 19-23
Abstract:
It is generally believed that superconducting materials are divided into two classes: `conventional' and `unconventional'. Conventional superconductors (e.g. the elements and thousands of alloys including MgB2) are described by conventional London-BCS-Eliashberg electron-phonon theory. There is no general agreement as to what mechanism or mechanisms describe `unconventional' superconductors such as the heavy fermions, organics, cuprate and pnictide families. Instead, I will argue that there is a single mechanism of superconductivity for all materials. This mechanism differs from the conventional mechanism in several fundamental aspects: in particular, it says that superconductivity is driven by lowering of kinetic rather than potential energy of the charge carriers, and it requires conduction by holes rather than electrons in the normal state. Furthermore I will argue that this mechanism can explain the Meissner effect, exhibited by all superconductors, and that the conventional mechanism cannot. Superconductivity in several different classes of materials will be discussed in the light of these concepts, as well as materials criteria necessary to achieve high temperature superconductivity.

Kinetic energy driven superfluidity and superconductivity and the origin of the Meissner effect

New3SC9, Frascati, Rome, Italy, September 16-20, 2012
Abstract:
Superfluidity and superconductivity have many elements in common. However, I argue that their most important commonality has been overlooked: that both are kinetic energy driven. Clear evidence that superfluidity in 4He is kinetic energy driven is the shape of the lambda transition and the negative thermal expansion coefficient below TÎŧ. Clear evidence that superconductivity is kinetic energy driven is the Meissner effect: I argue that otherwise the Meissner effect would not take place. Associated with this physics we predict that superconductors expel negative charge from the interior to the surface and that a macroscopic spin current exists in the ground state of superconductors (spin Meissner effect). We propose that this common physics of superconductors and superfluids originates in rotational zero point motion. This view of superconductivity and superfluidity implies that rotational zero-point motion is a fundamental property of the quantum world that is missed in the current understanding.

A unified description of high temperature superconductors,
low temperature superconductors, and superfluid 4He

UC Irvine Condensed Matter Seminar, November 28th, 2012
Abstract:
Progress in science often occurs when seemingly disparate phenomena are found to be describable within a unified framework. However, in the field of superconductivity just the opposite has occurred in the last 40 years: to explain newly discovered superconductors such as heavy fermion compounds, organics, borocarbides, high Tc cuprates, pnictides, non-magnetic oxides, sthrontium ruthenate, etc., many different scenarios have been proposed, distinct from each other and from the universally accepted BCS-electron-phonon theory to describe "conventional" superconductors such as the elements. Instead, I will present a unified description of superconductivity that applies to all superconducting materials. It explains many observations including well known phenomena in "conventional" superconductors that are thought to be understood but I argue are not at all understood in the conventional framework such as the Meissner effect, and predicts new phenomena such as a spin Meissner effect. It also provides guidelines in the search for new high temperature superconductors. Within this description, superconductivity in all materials and superfluidity in 4He are driven by the same physics, lowering of quantum kinetic energy.

High temperature superconductivity:
a scientific crisis awaiting a paradigm shift

Penn State Physics Special Seminar, December 10th, 2013
Abstract:
High temperature cuprate superconductors were discovered 27 years ago, and there is no consensus to date on the origin of the phenomenon. Many other families of superconducting materials have been discovered in the last 40 years that do not fit the conventional framework. A consequence of this is that there are no useful theoretical guidelines in the search for new higher Tc superconducting materials, despite claims to the opposite. I argue that the field is in crisis, and that the reason for this crisis is the unwillingness of the scientific community to consider the possibility that low temperature "conventional" superconductors are not well understood either. I argue that well-known phenomena such as the Meissner effect and the London moment are not explained by the conventional theory of superconductivity. I will describe work by our group started 25 years ago that aims to describe all superconducting materials within the same framework. Within our theory of "hole superconductivity", superconductivity is driven by lowering of quantum kinetic energy of the charge carriers, and can only occur if the carriers in the normal state have hole-like character. The theory provides simple and intuitive explanations for the Meissner effect and the London moment and predicts new phenomena in superconductors as yet unobserved, such as a "Spin Meissner effect". It also provides guidelines in the search for new high temperature superconductors, and reveals an unrecognized deep connection between superconductivity and superfluidity in 4He.

Condensed-Matter Physics & Materials Science Seminar, Brookhaven National
Laboratory, February 12th, 2014
Abstract:
Dynamic Hubbard models are simple extensions of the conventional Hubbard model that incorporate the generic fact that electronic orbitals in atoms expand under double electron occupancy, due to electron-electron repulsion. These models are electron-hole asymmetric and lead to superconductivity when electronic energy bands are almost full. Notably, the vast majority of superconducting materials exhibit positive Hall coefficient in the normal state, suggesting that this physics plays a role. Superconductivity described by these models is kinetic-energy-driven, and the superconducting ground state exhibits macroscopic charge inhomogeneity and an electric field in the interior. We predict that this physics takes place in superconducting materials and discuss optical and electron holography experiments that can detect it. These models also explain the Meissner effect and the London moment in a straightforward way.

High temperature superconductivity:
a scientific crisis awaiting a paradigm shift

CCNY Physics Colloquium, March 5th, 2014
Abstract:
High temperature superconductors were discovered 27 years ago (1986), and there is no consensus
to date on the mechanism that drives them, other than it is NOT the BCS electron-phonon
mechanism generally believed to explain low temperature "conventional" superconductors.
Several other families of superconducting materials have been discovered in the last 40 years that
do not fit the BCS framework. I argue that the field is in crisis, and will only make progress once
it is recognized that low temperature "conventional" superconductors are not well understood
either [1]. I will describe work by our group started 25 years ago that aims to describe all
superconducting materials within the same framework [2]: the theory of ``hole superconductivity''
proposes that only hole carriers can give rise to superconductivity, driven by lowering of quantum
kinetic energy. It provides a simple and intuitive explanation for the Meissner effect, predicts new
phenomena in superconductors as yet unobserved such as a "Spin Meissner effect" and the
existence of an electrostatic field in the interior of superconductors, it provides guidelines in the
search for new high temperature superconductors, and reveals an unrecognized deep connection
between superconductivity and superfluidity in 4He.
[1] "BCS theory of superconductivity: it is time to question its validity", Physica Scripta 80, 035702 (2009)
[2] References in: http://physics.ucsd.edu/~jorge/hole.html

Dynamic Hubbard model, high temperature superconductivity and the Meissner effect

Donostia International Physics Center, San Sebastian, Spain, July 4th, 2014
Abstract:
Dynamic Hubbard models describe the physical fact that atomic orbitals expand with increasing electronic occupation, unlike the conventional Hubbard model that ignores this fact. I will show that dynamic Hubbard models lead to high temperature superconductivity driven by lowering of electronic kinetic energy, and to charge inhomogeneity in the normal state, a characteristic feature seen in high temperature superconducting materials. I will also argue that dynamic Hubbard models can explain the Meissner effect and the London moment seen in all superconductors, while models where superconductivity is associated with lowering of the electronic potential energy cannot.
References in:
http://physics.ucsd.edu/~jorge/hole.html

EMRS Fall Meeting 2014, September 15 - 19, 2014, Warsaw, Poland
Abstract:
Dynamic Hubbard models describe the fact that atomic orbitals are not rigid but expand with increasing electronic occupation. The carriers described by these models when the band is almost full are small electronic polarons dressed by the atomic charge expansion and contraction as they hop from site to site with an increased effective mass and reduced quasiparticle weight. These models predict superconductivity driven by lowering of kinetic energy when a band is almost full (hole carriers), with higher Tc the more negatively charged the ions are. They give rise to negative charge expulsion from the interior to the surface and to charge inhomogeneity and electronic phase separation in the strong coupling regime, to asymmetric tunneling with larger current for a negatively biased sample, to negatively charged grain boundaries, and to multigap behavior with the smaller gap associated with electron-like carriers. We point out that high temperature superconductors such as cuprates, pnictides and magnesium diboride exhibit many of these features. More generally, superconducting materials described by dynamic Hubbard models would often exhibit lattice instabilities, a positive Hall coefficient in the normal state (Chapnik's rule), a small volume per conduction electron (Meissner-Schubert diagram), a magnetic moment parallel to their angular velocity if put into rotation (London moment), and expulsion of magnetic fields due to the expulsion of negative charge (Meissner effect).
References in:
http://physics.ucsd.edu/~jorge/hole.html

A new conception of superconductivity that
is consistent with Faraday's law

Temple University Physics Colloquium, Sept. 29th, 2014
Abstract:
It was pointed out by G. Lippmann in 1919 that a metal cooled into the superconducting
state in the presence of an applied magnetic field would `freeze in' the magnetic field
lines in accordance with Faraday's and Lenz's laws. Experiments by Onnes and Tuyn
(1924) on superconducting spheres were consistent with this basic physical principle.
However, 20 years later Meissner and Ochsenfeld proved Lippmann, Onnes and Tuyn
wrong: superconductors were found to expel magnetic fields. Why were Onnes and Tuyn
wrong? Because to save on the amount of He needed for cooling they had used hollow
rather than solid spheres. Why was Lippmann wrong? This has remained unexplained for
the past 95 years: London's and BCS theories that claim to explain the Meissner effect
are inconsistent with Faraday's law. In this talk I will present a new conception of
superconductivity that is consistent with Faraday's law, explains why Lippmann was
wrong, why cuprates and MgB2 are high temperature superconductors, why most
superconductors have positive Hall coefficient, and how to find new superconductors.
References in:
http://physics.ucsd.edu/~jorge/hole.html

Alternative London electrodynamics, hole superconductivity, and the origin of the Meissner effect

M2S, Geneva, August 23-28, 2015
(Link to talk here (pdf, 9.7MB))Abstract:
An electrodynamic theory of superconductors that allows for the presence of electrostatic fields in their interior was proposed initially by the London brothers in 1933 [1] but discarded by them shortly thereafter in favor of the one generally accepted to this date. I will argue that their original theory is closer to the truth. The theory of hole superconductivity [2], proposed to apply to all superconductors, is based on the fundamental charge asymmetry of matter and predicts that superconductors expel negative charge from their interior to the surface, resulting in macroscopic charge inhomogeneity and an outward-pointing electric field in the ground state of superconductors. The electrostatic energy cost is paid by lowering of quantum kinetic energy. The microscopic Hamiltonian is a dynamic Hubbard model [3], describing the expansion of atomic orbitals upon double electronic occupancy. Modified London equations in the charge [4] and spin sectors [5] and resulting predictions that can be tested experimentally are discussed. It is argued that the theory is consistent with existing experiments, provides a unified explanation for
high and low temperature superconductivity [6,7], and indicates that high temperature superconductivity results from holes conducting through closely spaced negatively charged anions [8]. Unlike the conventional theory, it provides a dynamical explanation of the Meissner effect.[9,10]
[1] F. London and H. London, The Electromagnetic Equations of the Supraconductor, Proc. Roy. Soc. A 149, 71 (1935).
[2] References in http://physics.ucsd.edu/~jorge/hole.html.
[3] J.E. Hirsch, Dynamic Hubbard model for solids with hydrogen-like atoms, Phys. Rev. B 90, 104501 (2014) and references therein.
[4] J.E. Hirsch, Electrodynamics of superconductors, Phys. Rev. B 69, 214515 (2004).
[5] J.E. Hirsch, Electrodynamics of spin currents in superconductors, Ann. Phys. (Berlin) 17, 380 (2008).
[6] J.E. Hirsch, Materials and mechanisms of hole superconductivity, Physica C 472, 78 (2012).
[7] J.E. Hirsch and F. Marsiglio, Hole superconductivity in H2S and other sulfides under high pressure, http://arxiv.org/abs/1412.6251 (2014).
[8] J.E. Hirsch, Hole Superconductivity, Phys.Lett. A134, 451 (1989).
[9] J.E. Hirsch, Dynamic Hubbard model: kinetic energy driven charge expulsion, charge inhomogeneity, hole superconductivity, and Meissner effect, Physica Scripta 88, 035704 (2013).
[10] J.E. Hirsch, The origin of the Meissner effect in new and old superconductors, Physica Scripta 85, 035704 (2012).

The most important scientific discovery of
the year 1911 was not superconductivity

UBC Condensed Matter Seminar, December 3rd, 2015
Abstract:
Each of the four concepts in the title is related to its nearest neighbor concept(s): this is well understood and generally agreed upon. What is not generally agreed upon is that these four concepts are all intimately related to each other, on the contrary, this is at odds with the conventional understanding of superconductivity (BCS). There is in fact very little that is generally agreed upon in the field of superconductivity these days, where the number of new materials classes, new observed phenomena, and proposed new models and unconventional mechanisms has proliferated like mushrooms after the rain in recent years. I will present a unifying view of superconductivity for all materials involving the four concepts in the title [1,2], discuss materials examples and experimental observations that support this point of view, and propose that many observed properties that are generally believed to be intimately related to the superconductivity of particular materials classes but are not shared by other materials classes may in fact be unimportant ''side effects''.
[1] J.E. Hirsch, Journal of Physics and Chemistry of Solids 67, 21 (2006)
[2] J.E. Hirsch, Annalen der Physik 526, 63 (2014).

The mystery of the disappearing supercurrent of superconductors

UCSD Condensed Matter Seminar, April 13, 2016
Abstract:
A superconductor in a magnetic field has a surface supercurrent that prevents the magnetic field from penetrating its interior. When the system goes normal the supercurrent disappears. What happens to its kinetic energy and momentum?
An answer to this simple and fundamental question existed for 20 years. Then, experiments proved that answer wrong, reopening the question. No new answer was proposed in the subsequent 80 years until the present, so the question remains unresolved. This is because researchers are not aware that the question exists, it is an 'unknown unknown'.
In this talk I will propose an answer to this question that has fundamental implications, and an experiment to test its validity.

Usos y abusos del indice h para la evaluacion de investigadores

How to explain the Meissner effect without violating momentum
conservation

11th International Conference on New Theories, Discoveries, Applications
of Superconductors and Related Materials, Sep 11-16, 2016, Bled, Slovenia
Abstract:
When a metal in a magnetic field becomes superconducting a supercurrent starts to flow to expel the magnetic field from the interior. Where does the momentum of the supercurrent come from? When a superconductor carrying a supercurrent goes normal the supercurrent stops. Where does its momentum go? Conservation of energy and momentum are fundamental tenets of physics, and a valid theory of superconductivity has to satisfy both. I argue that conventional BCS-London theory satisfies energy conservation but violates momentum conservation in its description of the reversible phase transformation between normal and superconducting phases in the presence of a magnetic field. To satisfy momentum conservation it is necessary to assume that: (i) there is charge transfer in direction perpendicular to the normal-superconductor phase boundary when the phase boundary moves, and (ii) the normal state current carriers are holes rather than electrons. The latter is consistent with the fact that essentially all superconducting materials have positive Hall coefficient [1]. Conventional BCS-London theory of superconductivity does not have these physical elements, the alternative theory of hole superconductivity does [2].
[1] I.M. Chapnik, `On the empirical correlation between the superconducting $T_c$ and the Hall coefficient', Phys. Lett. A {\bf 72}, 255 (1979).
[2] References in
http://physics.ucsd.edu/~jorge/hole.html

What's wrong with the Hubbard model and the BCS theory of superconductivity

University of Alberta Condensed Matter Seminar, October 27, 2016
Abstract:
It is generally believed that BCS electron-phonon theory explains the "conventional" superconductivity of metallic elements and simple compounds. For high Tc cuprates and other so-called "unconventional" superconductors BCS theory is believed to be inadequate and a variety of new theories have been proposed based on the single band Hubbard model that takes into account strong on-site electron-electron repulsion. I will argue that both approaches are fundamentally flawed for the same reason: they assume electron-hole symmetry. I will propose that electron-hole asymmetry is the key to superconductivity and discuss the alternative theory of hole superconductivity [1] as a candidate to describe all superconducting materials. The microscopic physics is described by dynamic Hubbard models, which are simple extensions of the conventional Hubbard model that take into account the fundamental charge asymmetry of matter. The theory predicts that superconductivity is kinetic energy driven and that superconductors expel negative charge from the interior to the surface, resulting in an electric field in the interior and a spin current near the surface. In the colloquium the following day I will show that the Meissner effect exhibited by all superconductors is consistent with this theory and inconsistent with conventional BCS theory.
[1] References in http://physics.ucsd.edu/~jorge/hole.html.

Meissner effect in superconductors: an unrecognized puzzle

Umezawa Colloquium, University of Alberta,
October 28, 2016
Abstract:
Superconductivity, the flow of electric current with zero resistance in certain metals at low
temperatures, was discovered in 1911 by Kammerlingh Onnes. It took another 22 years for
Meissner and Ochsenfeld to discover the telltale property of superconductors that makes
them different from ''perfect conductors'': the spontaneous expulsion of magnetic fields
from the interior of a metal becoming superconducting. This ''Meissner effect''
is generally
believed to be explained by the conventional BCS-London theory of superconductivity
developed in 1957. Instead, I argue that the Meissner effect is an unrecognized anomaly,
an observation that cannot possibly be explained within the established paradigm and
requires a paradigm shift [1]. I point out that conventional BCS-London theory violates
Faraday's law, Lenz's law, Newtons' laws and the second law of thermodynamics in its
description of both the Meissner effect and the superconductor to normal transition in a
magnetic field. I argue that to explain the observed phenomena in a way that respects
these fundamental laws requires charge flow in direction perpendicular to the normal-
superconductor phase boundary, and requires that the normal state charge carriers have
hole-like character. The conventional theory of superconductivity does not possess these
physical elements. Instead, the alternative theory of hole superconductivity [2], proposed
in 1989 to explain high Tc superconductivity in cuprates and superconductivity in general,
does. The empirically observed unexplained correlation between superconductivity and
Hall coefficient [3] supports our point of view.
[1] T. S. Kuhn, ''The Structure of Scientific Revolutions'', University of Chicago Press,
1962.
[2] References in http://physics.ucsd.edu/jorge/hole.html
[3] I.M. Chapnik, ''On the empirical correlation between the superconducting T
c and the
Hall coefficient'', Phys. Lett. A 72, 255 (1979).

Why only hole conductors can be superconductors

Abstract:
The conventional theory of superconductivity says that charge carriers in a metal that becomes superconducting can be either electrons or holes. I argue that this is incorrect, for the following reason. All superconductors exhibit the Meissner effect, which implies that the superconductor-normal phase transition in the presence of a magnetic field is reversible. In the superconducting state there is a supercurrent, in the normal state there is no current. The supercurrent carries mechanical momentum, while there is no mechanical momentum in the electronic normal state. I will argue that in order to conserve mechanical momentum in the superconductor to normal transition in the presence of a magnetic field it is necessary that the normal state charge carriers are holes.

Spinning superconductors and ferromagnets

Physics of Magnetism 2017 (PM'17), Poznan, Poland, June 26-30, 2017
Abstract:
When a magnetic field is applied to a ferromagnetic body it starts to spin (Einstein-de
Haas effect). This demonstrates the intimate connection between the electron's magnetic
moment μB = eℏ/2mec, associated with its spin angular momentum S = ℏ/2,
and ferromagnetism. When a magnetic field is applied to a superconducting body it
also starts to spin (gyromagnetic effect), and when a normal metal in a magnetic field
becomes superconducting and expels the magnetic field (Meissner effect) the body
also starts to spin. Yet according to the conventional theory of superconductivity
the electron's spin only role is to label states, and the electron's magnetic moment
plays no role in superconductivity. Instead, within the unconventional theory of hole
superconductivity [1], the electron's spin and associated magnetic moment play a
fundamental role in superconductivity. Just like in ferromagnets the magnetization
of superconductors is predicted to result from an aggregation of magnetic moments
with angular momenta ℏ/2 [2]. This gives rise to a "Spin Meissner effect" [3], the
existence of a spin current in the ground state of superconductors. The theory explains
how a superconducting body starts spinning when it expels magnetic fields [4],
which we argue cannot be explained by the conventional theory, it provides a dynamical
explanation for the Meissner effect [5], which we argue the conventional theory
cannot do, and it explains how supercurrents stop without dissipation [6], which we
argue the conventional theory fails to explain. Essential elements of the theory of hole
superconductivity are that superconductivity is driven by lowering of kinetic energy
[7], which we have also proposed is true for ferromagnets [8], that the normal state
charge carriers in superconducting materials are holes, and that the spin-orbit interaction
plays a key role in superconductivity. The theory is proposed to apply to all
superconductors [9].
References:
[1] http://physics.ucsd.edu/jorge/hole.html,
[2] J.E. Hirsch, Europhys. Lett. 113, 37001 (2016),
[3] J.E. Hirsch, Europhys. Lett. 81, 67003 (2008),
[4] J.E. Hirsch, Phys. Rev. B 95, 014503 (2017),
[5] J.E. Hirsch, Physica Scripta 91, 035801 (2016),
[6] J.E. Hirsch, Europhys. Lett. 114, 57001 (2016),
[7] J.E. Hirsch, Int. J. Mod. Phys. B bf 25, 1173 (2011),
[8] J.E. Hirsch, Physica C 341-348, 211 (2000),
[9] J.E. Hirsch, Physica C 472, 78 (2012).